The present invention relates to particulate filters for diesel exhaust systems. More particularly, the present invention relates to particulate filter assemblies that can be incorporated into diesel exhaust treatment devices.
Because regulatory agencies have recently mandated the reduction of particulate emissions in diesel engines, there has been increased activity in the development of diesel particulate filters, that is, exhaust emission filters for diesel engines. The role of a typical diesel particulate filter is to trap and remove the particulate components of the diesel exhaust stream, which include diesel soot and aerosols such as ash particulates, metallic abrasion particles, sulfates, and silicates, to prevent their discharge from the tailpipe.
Diesel particulate filters should provide long-term operation without diminishing the filtration efficiency of the filter and performance of the engine. Factors related to the performance of diesel particulate filters include but are not limited to high temperatures (e.g., up to 1400° C.), capability to store soot and ash, pressure loss, low thermal mass, stability, and durability. In addition, manufacturing costs and assembly volume are important considerations.
The filtration is achieved by a porous structure (e.g., filter media) that allows transmission of the fluid phase but stops or captures diesel particulate matter larger than a threshold particle size. Variations in the filter's efficiency are a function of the pore size of the filter media and particle size of the diesel particulate matter thus, every filter has a finite capacity, and as the flow through a diesel particulate filter decreases exhaust backpressure increases, which in some instances is undesirable. Due to the low bulk density of diesel particulates, diesel particulate filters can quickly accumulate considerable volumes of soot. To prevent filter pore clogging that causes backpressure to increase, thereby increasing load on the engine, the trapped particulate material is burned from the filter by continuous or periodic oxidation in the process of regeneration.
Accordingly, it is desirable to provide a filter assembly that can vary in geometry and be capable of having accumulated particles removed therefrom.